Aluminum pipe wall thickness. fitting vs welded - Mountain Buzz
 



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Old 11-21-2014   #1
 
Great Falls, Montana
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Aluminum pipe wall thickness. fitting vs welded

I have been using an NRS frame for my WW boat. I love it, but I've been thinking of welding one together over the winter. It looks like most frames that utilize fittings (lopros, speed rail or similar) are schedule 40. I'm guessing the are thicker and heavier because they are compressed by the fitting. Can I go to a smaller wall thickness that will keep the strength since it will be welded together?

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Old 11-21-2014   #2
 
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Aluminum pipe wall thickness. fitting vs welded

I think they are thicker and heavier to work in big boats where the spans are greater. I don't think it's the compression with lo pros or speed fittings.


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Old 11-21-2014   #3
 
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so, is that to say that welded / engineered frames should have the same heavy walled thick aluminum tubing for large frames?
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Old 11-22-2014   #4
 
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No. I think NRS and DRE use a stock pipe that will work for small frames and large frames. Basically one size does it all. If your frame is going to be on a smaller boat and you are you using one of these frames then your frame is heavier then it needs to be. I think if you look many of the welded frames using smaller pipe are either narrow set ups or they are steel or square stock.
If you are doing a whitewater frame for day trips I think you could push the limits of smaller pipe. It's when you ask your frame to make long spans between tubes and hang fully loaded dry boxes and huge coolers off them that you need the heavier stuff. In which case square stock buys you strength.
I think Guy Henderson of White Water Machine Works gave some math to show the different strengths between round and square in another thread. And hopefully some qualified frame welders chime in here to give some value. I am not one.


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Old 11-24-2014   #5
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The biggest difference between NRS frames and most other commercial welded frames is diameter. NRS uses 1 1/4" pipe and most welded frames are made from 1 1/2" pipe. The wall thickness is the same for either pipe, about .140". Diameter for 1 1/4" pipe is close to 1 5/8" and the diameter for 1 1/2" pipe is close to 2". Schedule 40 pipe is very common and relatively inexpensive. Thinner wall material is probably going to be difficult to find and more expensive.

p.s. NRS says there pipe is 1 5/8" OD and 1 3/8" ID giving only a 1/8" wall thickness so it falls somewhere between SCH30 (.117") and SCH40 (.140")pipe.
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Old 11-27-2014   #6
 
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Yes, for welding you can go with a smaller wall thickness and a porportionally smaller unit weight and cost. However, the pipe diameters and wall thicknesses have a buckling criteria aspect ratio that you want to pay respect to. At such diameter to thickness ratios, the pipe will buckle before it bends. Sch 40 pipe is generally a compact section which means it will bend without buckling at 3 diameters. Sch 5 will require internal support to do the same geometry. Temper and alloy will also affect the mechanism.
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